Abstract : Water use pattern of Tectona grandis planted at lowland forest assessed. The assessment was made for a different tree size of Tectona grandis. Two sizes selected were 16cm and 38 cm in diameter at breast height (dbh). Sapflow meter used to assess the sap velocity rates within 24 hours. Diurnal sapflow of Tectona grandis shows that mean velocity is high during day time compared night time. Small diameter has high sapflow compared to that of bigger diameter. A flow rates was high at the inner layer and less at outer layer for smaller tree. The variation was vice versa when the tree getting bigger.